class People(object):
    address = '山东' #类属性
    def __init__(self):
        self.name = 'xiaowang' #实例属性
        self.age = 20 #实例属性

p = People()
p.age =12 #实例属性
print(p.address) #正确
print(p.name)    #正确
print(p.age)     #正确

print(People.address) #正确
print(People.name)    #错误
print(People.age)     #错误